Matthew Poole and continuators on Leviticus 24:7

7 And thou shalt put pure frankincense upon each row, that it may be on the bread for a memorial, even an offering made by fire unto the LORD.

Unmixed and uncorrupted, or of the best sort.

Or, to the bread, or for the bread, to wit, to be burnt before the Lord instead of the bread which could not conveniently be offered to God in that manner. And this was done every time that the bread was changed.

For that part which properly belonged to God, whereas the rest belonged to the Priests. See on Levit. 2. 2.